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1. Field of the Invention
The invention relates to an electrical ignition method for internal combustion engines using an arrangement of a plurality of coils and of a magnetic generator that rotates synchronously with the engine and whose magnetic field at the same time passes periodically through the coils and generates therein a sequence of magnetic flux changes per rotation. In this process, a sequence of corresponding alternating-voltage half-waves is induced in the coils. These are used:
to charge an energy-storage element, that is discharged by actuation of an ignition switch via the primary-coil winding of an ignition transformer to trigger an ignition spark, and
to form the voltage supply of a microelectronic and/or programmable control (for example, a microcontroller) that is used to actuate the ignition switch in an ignition time instant as a function of the alternating-voltage half-waves detected and/or of the state of the internal combustion engine, for example its rotational position or rotational speed.
Furthermore, the invention relates to an ignition module suitable for performing the generic ignition method that has a magnetizable yoke core surrounded by a plurality of induction coils. The latter is constructionally and geometrically formed with a first and a second limb. The first limb is surrounded by a charging coil, whereas the second limb is surrounded at least by the primary and secondary coils of an ignition transformer. The energy-storage element is connected to the charging coil. Furthermore, the invention relates to a computer-program product having program-coding elements that are provided to execute the programmable control in order to implement the said method.
2. Description of the Related Art
To achieve a prolonged burn-time and a high spark energy, it is known from U.S. Pat. No. 4,538,586 to trigger the ignition spark in an angular range in which a flux change is effected precisely in the core of the ignition transformer by the magnet wheel of the magnetic generator rotating past. This induces a voltage in the secondary coil of the ignition transformer that is used to prolong the burn-time and to enhance the energy of the ignition spark. As a result, the fuel mixture in the internal combustion engine ignites more reliably. Specifically, it is proposed to use only a subsidiary flux change to prolong the burn-time, namely to trigger the ignition process at the start of the last, second-greatest alternating-voltage half-wave, from the point of view of amplitude magnitude, of a half-wave sequence. This achieves in any case a reduced attenuation of the main-flux change, which is used for the charging phase preceding the ignition.
From DE 38 17 187 C2, it is known to derive voltage half-waves that do not correspond to a forward direction by means of a diode in an ignition circuit and thereby to contribute to an uninterrupted, attenuated oscillation in the primary winding of the ignition transformer and in the charging capacitor discharging via it. This is intended to ensure a long spark burn-time. The circuit, which does not have a microelectronic and/or programmable control, causes, in a comparable way to U.S. Pat. No. 4,538,586 or U.S. Pat. No. 5,513,619, only small current consumption from the charging coil in the angular range of the ignition.
U.S. Pat. No. 5,513,619 (see, in particular, FIG. 6b therein) discloses an ignition module roughly of the type mentioned at the outset having a two-limb coil arrangement. The first limb in the rotational direction of the magnet wheel is surrounded by the ignition coil 124 and the subsequent, second limb is surrounded by a charging coil 126. Again, the ignition time instant takes place precisely when a voltage is induced in the secondary coil of the ignition transformer by magnetic flux change, as a result of which the burning of the ignition spark is maintained for as long as possible. However, this ignition system does not provide a possibility of flexibly adjusting the ignition time instant by flexible adjustment to various magnet wheel/yoke-core limb geometries of diverse internal combustion engine types.
DE 197 36 032 A1 discloses an ignition method roughly of the type mentioned at the outset, in which only the first limb in the direction of rotation of a two-limb, roughly U-shaped yoke core serves to promote and intensify the magnetic flux in the coils used to charge and trigger and also in the ignition transformer. To increase the technical reliability and safety, it is proposed to reset (xe2x80x9cRESETxe2x80x9d) or initialize the programmable control (for example, single-chip microcomputer) at least once to its initial state within every engine rotation in order to eliminate any adverse interference effects present externally in a sustained manner. Furthermore, the problem of guaranteeing the burn-time of the ignition spark is mentioned for the case where the activation signal of the microcontroller or of the control stops at the ignition switch during the capacitor discharge, for example owing to an interference effect due to the ignition spark. For this purpose, it is proposed to design the discharge-current circuit in such a way that the discharge of the energy-storage element is started by a short pulse from the microcontroller and the discharge process is maintained by a differentiating element until discharge is adequate. However, in that case, a special complexity of the specific circuit configuration of the differentiating element has to be implemented so that a residual charge still remains in the energy-storage element after termination of the discharge process, as it were, as xe2x80x9cfree chargexe2x80x9d for the next ignition spark triggering with then correspondingly prolonged ignition-spark time. Furthermore, it is again proposed to use only a subsidiary flux change to prolong burn-time, namely to trigger the ignition process at the start of the first alternating-voltage half-wave of a half-wave sequence. In any case, this makes possible a reliable orientation of the control in regard to angular position on the basis of the subsequent half-waves.
With regard to the further prior art, reference is made to U.S. Pat. Nos. 5,392,735, 4,924,831, 6,009,865, DE 40 17 478 and EP 0 394 656 B1.
In contrast, the object of the invention is to develop, avoiding the abovementioned disadvantages, a generic ignition method further in such a way that a prolonging of the ignition-spark burn-time (so-called top-up effect) can be achieved without additional circuit complexity with simultaneous optimization of the energy content of the ignition spark.
To achieve this in an ignition method having the features mentioned at the outset, it is proposed, according to the invention, that within one rotation, there is chosen, for the triggering of the ignition spark to prolong its burn-time, such a time interval in which the primary and/or secondary coil winding of the ignition transformer is specifically influenced by one of the magnetic flux changes and the amount or range of the magnetic flux change used to prolong the burn-time is greatest within the respective sequence. This departs from the method prevailing in the prior art mentioned at the outset of using only the last magnetic flux change of a sequence for triggering the ignition and for supplying the ignition transformer with energy. Instead, the ignition time instant or the position of the ignition angle relative to the flux change is set in such a way that, in this rotation-angle range or angular interval, the strongest magnetic flux change (so-called main flux change), triggered by the magnetic generator magnet wheel rotating past, comes into effect in the secondary coil of the ignition transformer. In a continuation of the inventive idea, said magnetic flux change can then be available solely for prolonging burn-time because energy does not then have to be drawn either from the coils for charging the energy-storage element or for supplying voltage to the microcontroller. This makes possible a continued burning of the ignition spark over a spark gap with a maximum current or with maximum spark energy.
Within the scope of an inventive alternative, the prolonging of the burn-time and the inductive topping-up of the ignition energy can also be effected in that, in the chosen time interval of the magnetic flux change, use of the alternating-voltage half-waves has been or is excluded at least for the formation of the voltage supply to the microcontroller or to the control. Since the effect of a magnetic flux change and, consequently, induced alternating-current half-wave is in this way no longer diminished by energy withdrawal for the microcontroller voltage supply, a prolonging of the burn-time already improved compared with the prior art can be produced in conjunction with a flexibly programmable ignition-time adjustment.
An advantage achievable jointly with the two inventive alternatives is that even less energy is necessary to initiate the ignition spark. As a further advantageous consequence, an ignition capacitor having a comparatively low capacitance, for example 0.47 xcexcF instead of 0.68 xcexcF or 1 xcexcF, can be used as energy-storage element, which results in an advantage in regard to overall volume and costs.
According to a further refinement, the position of the ignition time instant or of the ignition angle referred to the magnetic generator rotation is correlated with the magnetic flux changes passing through the coils in such a way that, in the time interval comprising the ignition time instant, use of the alternating-voltage half-waves has been or is excluded also for charging the energy-storage element. Consequently, the magnetic flux change that is possibly the strongest (greatest size or extent) can be used solely to prolong the burn-time.
In accordance with a refinement of the invention, a coil arrangement is used that extends constructionally and geometrically over two distinct limbs, preferably of an iron or yoke core, preferably U-shaped. In this case, the first and then the second magnetic pole of the magnetic generator are each consecutively moved past the first and then the second limb within a full rotation. Advantageously, in this case, the magnetic flux change taking place in the second limb and at the third point therein per rotation or sequence is fed directly to the ignition transformer. The effect achieved is the efficient prolonging of the ignition-spark burn-time. In addition, the coil interactions can be reduced by the distribution of the coils over two limbs (remote from one another), as a result of which the alternating-voltage half-waves produced by the coils, in particular, are attenuated less during energy withdrawal.
This pursues the path to a further inventive development, namely to utilize the magnetic flux changes occurring in the first and second limb per rotation or sequence in each case at the second point in time or resultant alternating-voltage half-waves across the coils of the respective limbs in parallel and/or roughly simultaneously to charge the energy-storage element and to supply voltage to the control. Because of the arrangement on different limbs, mutual attenuation of the charging coil and of the voltage-supply coil takes place only to a considerably reduced extent. On this basis, a further development is expedient according to which, to form the voltage supply, one of the alternating-voltage half-waves of the second limb is utilized within the respective rotation or sequence in that time interval in which the magnetic flux change and/or resultant half-wave having the greatest size or extent occurs in the first limb. The latter can be used in an advantageous development to charge the energy-storage element. The voltage supply to the control therefore takes place during the second-strongest or third-strongest magnetic flux through the ignition coil and the charging phase of the energy-storage element, in particular ignition capacitor, the strongest flux change taking place in the charging coil.
With particular advantage, the energy-storage element, in particular ignition capacitor, can be charged within the respective rotation or sequence with two half-waves, preferably the second, in particular strongest/greatest, and fourth or last of a half-wave sequence. As a result, the energy-storage element is already precharged at the end of a half-wave sequence and is further charged in the next half-wave sequence with the second and, in particular, strongest half-wave sequence. The energy-storage element therefore experiences the main charge as a result of the main flux change in the charging coil. This is expedient, particularly at high rotational speeds, where the maximum charging of the energy-storage element is no longer achieved owing to the shorter rotation time.
Using the two-limb coil arrangement, it is possible, on the basis of the invention, to utilize the respective strongest magnetic flux change in each limb, on the one hand, to charge the energy-storage element and, on the other, to top up energy in the secondary coil in the ignition time range.
A further advantage of the two-limb coil arrangement emerges from the inventive development according to which alternating-current half-waves of the coils of the two limbs are fed to the control for processing and, in this process, the half-waves of different coils are set in time relationship to one another within the control. From this, the control can determine by means of suitable evaluation software, for example, the direction of rotation, the rotational position and/or the rotational speed of the magnetic generator or of the internal combustion engine. Depending on this, the adjustment and the triggering time instant for the ignition spark can in turn be calculated or flexibly set within the control.
In the starting rotational-speed range, the rotational speeds and the corresponding magnetic flux changes are relatively low, with the result that an economical utilization of the induced electrical energy is offered. The invention therefore strives to help to supply the control with operating voltage only over a minimum angular range prior to the ignition time instant. Correspondingly, according to an inventive development, the ignition time instant is determined, adjusted and/or triggered within a time interval by means of the control, at any rate if the internal combustion engine is running in the starting rotational-speed range, which time interval corresponds as a maximum to a rotation of the magnetic generator by up to about 80xc2x0. Expediently, all the data relevant to triggering the ignition time instant are obtained from the half-wave signals of the control within this relatively small angular range and evaluated.
Depending on different types of internal combustion engine, the spacing of the ignition time instant from top dead center in the working rotational-speed range may differ from that in the starting rotational-speed range. In order, nevertheless, to be able to use similarly constructed coil arrangements and ignition modules for different engines, flexibility of the angle-related ignition triggering has to be strived for by the respective ignition module. In this regard, it is advantageous if, according to an expedient inventive development, the ignition time instant is adjusted or triggered, per rotation or within the respective sequence, within a time interval that is defined or limited by the magnetic flux changes or resultant alternating-voltage charging half-waves having the greatest size or extent or the greatest amplitude within a sequence and also by the respective subsequent magnetic flux changes or alternating-voltage charging half-waves. In that case, it is of particular advantage to utilize magnetic flux changes or any second limb of the coil arrangement. Consequently, the ignition triggering can be flexibly programmed in this development. Therefore, as is disclosed above, a particular magnet wheel position relative to the ignition transformer is necessary for an optimally high-energy ignition spark. For a differing angular distance with respect to the starting curve, the triggering element would have to be advanced mechanically without the invention. On the basis of the invention, the criterion for the ignition time instant can be chosen or programmed easily, for example, by means of a threshold decision that can be triggered earlier on the basis of the input signals of the control derived from the coils.
According to DE 197 36 032 A1 mentioned at the outset, it is advantageous to set the control periodically to a defined (initial) state. For this purpose a RESET signal is generated by hardware means external to the control depending on the respective magnetic generator magnet wheel position and inputted into the control, as a result of which reinitialization is triggered. This has to take place outside the time interval for the calculation and adjustment of the ignition time instant since all the control activities have to be concluded by then and only start again for a repeat ignition cycle. Data stored within the control can, however, be maintained beyond the time instant of the RESET signal/reinitialization because the volatile working memory of the control (RAM) does not need to be erased in this process. In contrast, the invention proposes resetting and/or reinitializing the control synchronously with respect to predetermined positions of the internal combustion engine and of the magnetic generator synchronized thereto to an initial state at least twice per rotation. Simultaneously, an internal control time counter or a time counter interacting with the control is started in each case. If its count results are correlated with the occurrence in time of the alternating-voltage half-waves detected by the control, the direction of rotation, rotational position and/or rotational speed of the magnetic generator can be determined therefrom by means of the control or its arithmetic logic unit. These information items can be used as (functional) arguments for determining the ignition time instant, optionally with the aid of previously stored tables. The resetting or reinitialization at predetermined (rotational-angle) positions of the internal combustion engine or of the magnetic generator coupled thereto, for example, at sixty angular degrees before top dead center of the reciprocating piston and at the top dead center itself results in a first orientation and information item relating to the respective rotational angular position for the signal and data processing proceeding in the control. The fine angular position can then also be determined with the aid of the said time counter or time generator in combination-with threshold value decision circuits that can be programmed and sampled by the control.
In accordance with a further development of the idea of resetting twice per rotation, the latter takes place in each case in the half-waves that are used for the voltage supply to the control. In particular, to generate the RESET signals the first edge or, alternatively, the peak points of the half-waves can be used in each case. An advantage in conjunction with the coil arrangement distributed over two limbs can be achieved in that the control detects that the coil signals of different limbs have exceeded or dropped below the threshold and determines their relative position in time with respect to one another.
To increase the application flexibility of ignition modules having the features mentioned at the outset in regard to different magnet wheel/yoke limb geometries and simultaneously to achieve an optimal ignition spark burn-time, it is proposed within the scope of the general inventive idea to provide a microelectronic and/or programmable control for the ignition module that is connected to the coils for sampling, processing and/or rating their alternating-voltage half-waves and is designed to actuate the ignition switch as a function of the alternating-voltage half-waves. In this case, an input of the control provided for the voltage supply is connected to a coil of the second limb via a rectifier. The latter measure achieves the result that a charging coil mounted, for instance, on the first limb, is less impaired by the spatial distance from a voltage-supply coil on the second limb, preferably at its unsupported end, during the generation of the charging energy for the energy-storage element.
Furthermore, there is within the scope of the general inventive idea a computer program having program code elements that produce, during loading into a program memory of the control and starting of the computer program, electronically read-out control signals that interact with a processor of the control in such a way that the abovementioned method steps that can be executed by the control are implemented. Furthermore, there is, within the scope of the general inventive idea, a digital memory or carrier medium that comprises the program code elements and keeps them ready for the program memory of the control.